Warning: Spoilers follow
In the novel, Goldstein, rumored to be a former top member of the ruling political party Ingsoc, he had broken away early in the movement and ran an organization known as "The Brotherhood" dedicated to the fall of the Party. However, in the course of the novel, we learn that we will never know whether either "The Brotherhood" or Goldstein himself actually ever existed.
Each member of "The Brotherhood" is required to read a book supposedly written by Goldstein, The Theory and Practice of Oligarchical Collectivism, and each person is said to have 3 or 4 contacts at one time which are replaced as people disappear, so that if a member is captured, he can only give up 3 or 4 others. Of Jewish descent, Goldstein is always the subject of the "Two Minutes Hate," a daily, 2-minute period beginning at 11:00 AM at which some image of Goldstein is shown on the telescreen (a one-channel television with surveillance devices in it). It is thought that the presence of an opposition - Goldstein - to Big Brother was a pure construction to ensure that support and devotion towards Big Brother was continuous.
The character of Goldstein is considered to be modeled on Leon Trotsky.
Emmanuel Goldstein is also the pseudonym of Eric Corley, editor of 2600 The Hacker Quarterly.